Study of Hafnium Dioxide (HfO 2 ) by Atomic Layer Deposition (ALD)

1. Study of Hafnium Dioxide (HfO2) by Atomic Layer Deposition (ALD) Yen Chin Woo Master of Science in Electrical Engineering Instructor Professor Beth Stadler December 6, 2005

2. Outline • Background • Choice of High-κ Dielectric • Comparison of Deposition Methods • Advantages of Atomic Layer Deposition • Precursors • Fabrication Method • Film structure • Applications of Atomic Layer Deposition

3. -Si -Si SiO2 SiO2 NMOS PMOS Background Ultra Large Scale Integration Physical Limitation • CMOS: Two types of transistors • NMOS: negatively doped silicon, rich in electrons. • PMOS: positively doped silicon, rich in holes (the DUAL of electrons). • Downsizing of CMOS requires smaller dimensions • SiO2 (κ = 3.9) is currently used as dielectric layer • Problem • Oxide thickness less than 2.3nm produces considerable off-state leakage current • High leakage currents: result of electron tunneling through SiO2 film • Other reliability issues • Solution • ↑ capacitance of the dielectric layer lead to ↓ current leakage • where C = κεA/d Thompson, Scott, MOS Scaling: Transistor Challenges for the 21st Century, Intel Tech. J., 1998

4. Choice of High-κ Dielectric Material 5 conditions - • High enough dielectric constant κ • Stable - no reaction with Si • Oxides with high heat of formation • Preferred –HfO2, Zr, Y, La, Al • Stable up to 1050°C • Low diffusion • Wide band gap for low leakage • Good interface, low impurities, traps Source: J. Robertson * HfO2 is the most promising candidate http://www.cambridgenanotech.com

5. Comparison of Thin Film Deposition Methods ALD = atomic layer deposition, MBE = molecular beam epitaxy. CVD = chemical vapor deposition, PLD = pulsed laser deposition. http://www.cambridgenanotech.com

6. Advantages of Atomic Layer Deposition Mikko Ritala and Markku Leskelä, “Atomic layer epitaxy - a valuable tool for nanotechnology?” Nanotechnology10 (1999) 19-24

7. Precursors • Must be volatile and thermally stable to ensure efficient transportation • Must chemisorb onto surface or rapidly react with surface • Cannot self-decomposes • Should not etch or dissolute into the film or substrate • Vapor Pressure of Precursors • Must be high enough to completely fill the deposition chamber • Precursor Choices: • Hafnium (IV) Chloride (HfCl4) + H2O • Hafnium (IV) Iodide (HfI4) + H2O • Hafnium Tetrakis(enthylmethylamide) + H2O • Hafnium (IV) Tert-butoxide + H2O • Hafnium Tetrakis(diethylamido) + H2O • Hafnium Tetrakis(dimethylamido) + H2O

8. Fabrication Method Example: Overall reaction HfCl4 + 2H2O → HfO2 + 4HCl

9. HfCl4+H2O HfI4+H2O 300°C 300°C r.m.s = 2.3nm r.m.s = 1.8nm Hf[N(CH3)(C2H5)]4 + H2O 200°C 300°C r.m.s = 7.9nm r.m.s = 3.9nm Film Structure [1] Kaupo Kukli, Mikko Ritala, Timo Sajavaara, Juhani Keinonen and Markku Leskelä “Comparison of hafnium oxide films grown by atomic layer deposition from iodide and chloride precursors,”Thin Solid Films 416(2002) 72-79 [2]Kaupo Kukli, Mikko Ritala, Timo Sajavaara, Juhani Keinonen and Markku Leskela, “Atomic layer Deposition of Hafnium Dioxide Films from Hafnium Tetrakis(enthymethylamide) and Water,” Chem. Vap. Deposition 8 (2002) 199-204

10. Applications of ALD Financial Viability in the coming years: • Transistor Gate Dielectrics • MEMS • Opto-electronics • Diffusion Barriers • Flat-Panel Displays • Organic Light Emitting Diodes (OLED) • Interconnect Seed Layer • DRAM and MRAM dielectrics • Embedded capacitors • All thin films (<90nm) • Electromagnetic recording heads

11. “Q & A” Thank You

12. Allowable Temperature Window